Hydraulic brakes used to brake the wheels of air-craft generally comprise a ring having multiple cavities in which brake actuators are connected in a removable manner. Each of the actuators comprises a sleeve which is sealingly connected in one of the cavities of the ring and in which a piston is sealingly slidably mounted along a sliding axis.
The ring distributes pressurized hydraulic fluid into all of its cavities, a fluid which acts on the piston to cause it to be extended and to apply a braking force on the friction elements extending opposite the ring, including rotors which rotate with the wheel and stators which are fixed in terms of rotation.
The piston generally has an operational path which it follows during the application of a braking force. This operational path, in the order of several millimeters, is sufficient to permit the application of the braking force on the friction elements, and the return of the piston so as to permit the free rotation of the rotors. To this end, a spring extending inside the piston ensures the return of the piston as far as a retracted position when the braking force is no longer applied.
However, as the friction elements are progressively worn as a result of the repeated action of braking forces, it is important that the piston is always located in the vicinity of the friction elements. To achieve this, it is known to provide the brake actuators with a wear compensating device which extends inside the piston.
Wear compensating devices are known, said wear compensating devices comprising a mobile stop which is slidably mounted with friction along the sliding axis on a central rod extending in the piston and which defines the retracted position of the piston. During the application of a braking force, the piston is pushed toward the friction elements and in this case drives the mobile stop therewith, overcoming the friction between the rod and the stop which causes the mobile stop to move forward on the rod. When the force is released, the spring returns the piston to the new retracted position which has moved forward due to the advance of the mobile stop relative to the rod.
The friction may be distributed as follows: the mobile stop comprises a radially deformable bushing which cooperates at one distal end with an olive attached to a distal end of the central rod so as to be deformed by said olive.
However, the mobile stop tends to move around the olive during the displacement thereof along the sliding axis. The proximal end of said mobile stop then rubs against the central rod which may cause the formation of undesirable grooves on the central rod. More specifically, the proximal end of the piston is partially guided by the central rod of the wear compensating device, a seal being borne by the piston so as to extend between the central rod and the proximal end of the piston. Thus, during the displacements of the piston along the sliding axis, the seal regularly rubs against said grooves which ultimately causes a deterioration of the seal which impairs the sealed state of the actuator.